Meeting the current challenges of the US health care system for children will require novel and wide-ranging action-oriented research to improve the effectiveness, efficiency, and equity of health care. This renewal application harnesses the expertise of a dedicated, diverse, and experienced faculty with an 18-year history of leading successful AHRQ-funded post-doctoral NRSA training programs focused specifically on pediatric health services research. We now propose to substantially augment our current program (including its faculty, partnerships with families and health system stakeholders, and curriculum) to specifically focus on implementation science and reduction of health disparities. We will continue the core programmatic collaborations among Boston Children's Hospital, the Mass General Hospital for Children, and the Department of Population Medicine at Harvard Medical School. In addition, we will fully engage a new partner-the Institute of Healthcare Improvement-which will bring its internationally-recognized expertise in care improvement and implementation science to our trainees through curricular enhancements and research opportunities. Additional partnerships will include the National Institute for Children's Healthcar Quality for large-scale, ongoing projects dedicated to reducing health care disparities; diverse care delivery systems including local community health centers; the Harvard Medical School Center for Primary Care; and health insurers. We will also develop novel ways to include the voices of patients and parents in our training by incorporating them as program advisors and designing structured interactions of trainees with a newly formed parent resource group to ensure parent and patient perspectives in trainees' research. The program will support 7 stipends per year (4 first-year, and 3 second-year continuing postdoctoral fellows in the first year) to create a critical mass of trainees across subspecialties, areas of research, and methodological domains. In addition to participating in closely mentored research, each trainee will successfully complete the requirements of an MPH from the Harvard School of Public Health for core skills of biostatistics and epidemiology, and participate in advanced health services research methods training including a newly developed curriculum of improvement science and implementation science methods. An already well-developed program infrastructure and system for close tracking of trainees' progress will ensure the continuation of our record of graduating individuals who will lead relevant, applied health services research that translates into both improved care and health outcomes for the children we serve.